Medication compliance is the degree to which a medication is taken according to a prescribed treatment and is usually measured in terms of percent of doses taken over a given interval. It is estimated that thousands of people may die of treatable ailments because of poor adherence and a tenth of hospital admissions are associated with noncompliance at a healthcare services expense of approximately $15.2 billion annually. Medication compliance is also important in the context of clinical drug trials, geriatrics, and mental health/addiction medicine. For example, in a clinical drug trial it is desirable to know, with a high degree of certainty, the patient's compliance to a medication regimen, because without such knowledge the results from a clinical trial cannot be accurately interpreted or could even be misleading. In each case there is a clear and present need for relatively low-cost, automated technologies that can replace directly observed therapy (DOT), which is one known method of determining medication compliance. This known method tends to be costly and cumbersome since it depends on human labor.
An orally ingestible pill with an embedded passive microsystem disposed of via the gastrointestinal (GI)-tract and capable of communicating with devices external to the body can lead to an improved indirect method for monitoring a patient's adherence to a regimen. The current state of the art in passive microsystems for in-body communications does not fully address the fundamental challenges associated with severe signal attenuation inside human tissues, poor radiation properties of electrically small antennas, limited power for signaling and high path loss dependence on distance.
Known approaches utilize devices which are predominantly battery powered as at large distances the transmitted signals are severely attenuated inside the human body (i.e. the signal attenuation depends on various factors such as frequency of operation, tissue attenuation, electrical antenna size, mismatch losses, etc). Since batteries ultimately limit the potential for miniaturization (i.e. silicon devices can be orders of magnitude smaller), aspects of the present invention focus on passive microsystems. It will be appreciated, however, that the techniques described herein may also be applicable to battery powered systems.
In the context of passive devices, the operational range of biomedical devices inside the body is substantially limited (e.g., typically a few cm due to weak coupling, high tissue attenuation and/or human exposure limits to radio frequency (RF) fields). Traditional passive radio-frequency identification (RFID) transponders operating in the far-field suffer from space/frequency tradeoffs not suitable for miniaturized in-body communication. Since electrically large antennas in the far-field of operation are required to capture sufficient RF power to activate the transponder, devices with small antennas when operated at low frequencies suffer from poor radiation characteristics and when operated at high frequencies suffer from increased signal attenuation. Near-field transponders powered from low frequency magnetic fields have limited range, require multi-turn coils which are often wrapped around ferrite core materials to improve signal coupling, and suffer from power/bandwidth/size tradeoffs.